Subject: [PWE3] About C bit negotiation for P2MP PW

From: [email-masked]
Date: Tue, 20 Apr 2010 12:31:24 +0800

Hi Luca,
As we discussed at IETF 77 Anaheim, currently there is no CW negotiation 
for P2MP PW. I suggest to use LDP notification and mapping to do CW 
negotiation in draft-martini-pwe3-p2mp-pw-01. Because any leaf node will 
send an LDP notification to root node to indicate PW status. We can just 
use this procedure also to do CW negotiation.

In my opinion, CW negotiation is important for P2MP PW. If one of the leaf 
does not support CW, then root node will adjust to not support CW for P2MP 
PW. The above procedure can also be used for VCCV negotiation, the root 
and leaf node should align with the CC type. After all, three CC type are 
defined now.

BR
Lizhong

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From: Luca Martini <[email-masked]>
Date: Tue, 20 Apr 2010 15:10:47 -0600

Lizhong,

The current design direction is to not negotiate anything between the root , and the leafs. We simply notify the leafs of the proprieties of the PW, and if the Leaf cannot accept it, that portion of the PW is simply not enabled.

It is impossible to have two kind of leafs in the same p2mp tree. So it is not possible to negotiate the CW usage, as it's either all on, or all off.
If you need a mixed system, you can simply use two p2mp PWs, one with CW=on and one with CW=OFF and have the Leafs join the correct one.
 
In a p2mp PW I do not see a way to negotiate anything different between leaves at the dataplane level.

Thanks.
Luca

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From: [email-masked]
Date: Wed, 21 Apr 2010 10:26:22 +0800

Luca,
Please see my further comments in line below.

BR
Lizhong Jin

Luca Martini <[email-masked]> 
2010-04-21 05:10

To
[email-masked]
cc
[email-masked], [email-masked]
Subject
Re: About C bit negotiation for P2MP PW

Lizhong,

The current design direction is to not negotiate anything between the root 
, and the leafs. We simply notify the leafs of the proprieties of the PW, 
and if the Leaf cannot accept it, that portion of the PW is simply not 
enabled.

It is impossible to have two kind of leafs in the same p2mp tree. 
[Lizhong] Agree.

So it is not possible to negotiate the CW usage, as it's either all on, or 
all off.
[Lizhong] We can negotiate CW like this. If the CW configuration on root 
PE is PREFERRED, and advertise label mapping with C_bit=1 to all leaf PEs. 
But there maybe one of the leaf PE do not support CW=1. When this leaf PE 
receiving label mapping with C_bit=1, it will send an LDP notification 
with PW status "DOWN" to root PE, carrying FEC with C_bit=0. When root 
node receiving this LDP notification message with C_bit=0 and "DOWN" 
status, it will send label withdraw with wrong C-bit and send a new label 
mapping to all leaf PEs. After above procedure, P2MP PW will have only 
C-bit=0 to support.

If you need a mixed system, you can simply use two p2mp PWs, one with 
CW=on and one with CW=OFF and have the Leafs join the correct one.
 
In a p2mp PW I do not see a way to negotiate anything different between 
leaves at the dataplane level.

Thanks.
Luca

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From: Stewart Bryant <[email-masked]>
Date: Wed, 21 Apr 2010 08:58:35 +0100

lizhong jin
>
> [Lizhong] We can negotiate CW like this. If the CW configuration on 
> root PE is PREFERRED, and advertise label mapping with C_bit=1 to all 
> leaf PEs. But there maybe one of the leaf PE do not support CW=1. When 
> this leaf PE receiving label mapping with C_bit=1, it will send an LDP 
> notification with PW status "DOWN" to root PE, carrying FEC with 
> C_bit=0. When root node receiving this LDP notification message with 
> C_bit=0 and "DOWN" status, it will send label withdraw with wrong 
> C-bit and send a new label mapping to all leaf PEs. After above 
> procedure, P2MP PW will have only C-bit=0 to support.
A late joining system would cause a service disruption if it caused the PW to be taken down and reestablished, and doing a 1+1 migration may need more b/w than is available. It would seem to be better to set the tree up one way or the other and if a leaf did not like the parameters, it's owner should complain to the service provider.

Stewart

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From: [email-masked]
Date: Wed, 21 Apr 2010 16:12:37 +0800

Hi Stewart,
Your explaination makes sense. I will reconsider this. Thank you very 
much.

BR
Lizhong Jin

Stewart Bryant <[email-masked]> 
2010-04-21 15:58
Please respond to
[email-masked]

To
[email-masked]
cc
Luca Martini <[email-masked]>, [email-masked], [email-masked], 
[email-masked]
Subject
Re: [PWE3] About C bit negotiation for P2MP PW

lizhong jin
> procedure, P2MP PW will have only C-bit=0 to support.
A late joining system would cause a service disruption if it caused the PW 
to be taken down and reestablished, and doing a 1+1 migration may need 
more b/w than is available. It would seem to be better to set the tree up 
one way or the other and if a leaf did not like the parameters, it's owner 
should complain to the service provider.

Stewart